1. Field of the Invention
The present invention relates to an optical device wafer processing method for dividing an optical device wafer into individual optical devices along a plurality of crossing streets formed on the front side of a sapphire substrate constituting the optical device wafer, wherein the optical device wafer is formed by laminating gallium nitride compound semiconductors or the like, and the individual optical devices are respectively formed in a plurality of regions partitioned by the streets.
2. Description of the Related Art
A plurality of crossing division lines called streets are formed on the front side of a sapphire substrate to thereby partition a plurality of regions where optical devices such as light emitting diodes are respectively formed. An optical device wafer is formed by laminating gallium nitride compound semiconductors or the like on the sapphire substrate. The optical device wafer is divided along the streets to thereby obtain the individual optical devices, which are widely used in electric equipment.
As a method of dividing a platelike workpiece such as a semiconductor wafer, a laser processing method using a pulsed laser beam having a transmission wavelength to the workpiece has been proposed in recent years. In this laser processing method, the pulsed laser beam is applied to the workpiece along the streets in the condition where a focal point of the pulsed laser beam is set inside the workpiece in a subject area to be divided. In such a wafer dividing method using laser processing, the pulsed laser beam having a transmission wavelength to the wafer from one side thereof in the condition where the focal point is set inside the wafer, thereby continuously forming a modified layer inside the wafer along each street. By forming the modified layer along each street, the strength of the wafer along the modified layer is reduced. Accordingly, by applying an external force to the wafer along each street, the wafer can be divided into individual devices (see Japanese Patent No. 3408805, for example).
After laminating gallium nitride compound semiconductors or the like on the front side of the sapphire substrate to form the optical devices, the sapphire substrate becomes substantially unnecessary. Accordingly, the back side of the sapphire substrate is ground to reduce the thickness of the sapphire substrate before dividing the optical device wafer into the individual optical devices.